Cleanup snapshots when snapshot filter feature in aptly is ready

[ganwell]

Rotated snapshots are not needed and could be cleaned up. Repositories (e.g. Ubuntu) include all packages so a cleanup of snapshots wouldn't really help as the newest snapshot would still include all packages. Hence the aptly filter (only latest package) would need to be implemented.

Once this is implemented and snapshots are also cleaned up a aptly db cleanup would remove packages which are not references anymore.

Issue in aptly to be completed: https://github.com/adfinis-forks/aptly/issues/28

Tasks to be implemented in pyaptly:

• Using new filter option in mirror filter
• Delete snapshots which are not current